Precast concrete double tee joists are one of the most popular precast concrete floor framing systems. However, compared to open steel joists, standard concrete joists are heavy and do not allow mechanical and electrical equipment (i.e. HVAC systems, electrical wiring, plumbing and the like) to pass through them. Placing web openings in these joists to allow equipment to pass through them is a significant improvement, reducing the floor to floor height and overall building height. This reduced building height can result in significant economy in the cost of the building and in the mechanical and electrical systems installed therein. A further benefit of using joists with web openings is weight reduction. This weight reduction also results in reduced vertical gravity loads and horizontal seismic forces in the supporting beams, columns, and foundation.
Other researchers have experimented with precast, prestressed concrete beams having integral web openings. However, previous researchers have typically proposed rather involved procedures to design for the web opening, making the construction and use of these concrete joists difficult and costly. Consequently, the prior art has failed to develop a precast, prestressed concrete joist having web openings which may be efficiently manufactured to meet a wide variety of spans, spacing, and loading requirements.